On 6/9/2011 9:04 PM, W Davis wrote:
> Awhile ago, I had a sudden problem..driving home from work;
> all of a sudden, the alt light began to glow, dash lights went out, and the tach
> started going all over the place.
>> Long story short, I pulled the voltage regulator from the alternator, and simple
> visual
> inspection showed it was bad...replaced the v-reg with a new one I had, and all
> was
> well again, except I still have intermittent "whacky tach syndrome".
>> 1- from what source does the tachometer sense what it's reading?..is it the
> alternator?
>> 2- what might be the problem..the tach itself,, or the source from which it
> gets its' info?
>> Many thanks,
>> William in Fla
>> 1985 Jetta GL turbo diesel, my daily driver,
> running fine otherwise.
Yes, the OEM diesel tach works off the alternator, specifically a special terminal called
the W-terminal:
http://www.4crawler.com/Diesel/CheapTricks/Tachometer/index.shtml#OEMInstall
Basically an unfiltered tap off the raw alternator AC voltage.
Might be a loose connection or could be brushes inside the alternator or maybe an
intermittent diode that is connected to the W-terminal winding.
--
Roger